The invention relates to a method for operating an internal combustion engine comprising at least one combustion chamber, air inlet and gas exhaust valves and an injection valve by which an overheated and pressurized mixture, consisting of fuel vapor and water vapor is injected into the combustion chamber and wherein heating of the mixture is effected by hot exhaust gas leaving the engine.
A method of this kind is known from German patent reference DE 37 34 346-A. According to this method a pump for pressure elevation of the liquid fuel and a second pump for the water is proposed and the mixture is evaporated at a pressure above the maximum compression pressure. The fuel-vapor-water-vapor-mixture is fed to the injection valve at a temperature of substantially 430.degree. F. This reference gives us information on the absolute pressure level of the fuel-vapor-water-vapor-mixture.
German patent reference DE 39 24 013-A describes a similar method, which differs from the aforementioned method, because the pressure of the fuel-vapor-water-vapor-mixture is smaller than the maximum compression pressure in the cylinder at maximum power. In this reference the pumps for water and liquid fuel are designed so that the pressure for entering the evaporator is adjustable between 5 and 20 atm.
The purpose of both references is to create a method to inject fuel vapor and water vapor into an internal combustion engine at the same time to have available the fuel already in vaporized state when it is injected into the combustion chamber and to receive a homogeneous explosive mixture after mixing it with combustion air. It is well known in the art, that water vapor can reduce noxious gaseous components especially NO.sub.x or smoke particles in the exhaust gas and that the specific fuel consumption can be reduced thereby.
In German reference DE 42 18 104 A it is proposed, to inject over-heated water at a temperature of 700.degree. F. and about 223 atm into the combustion chamber of an internal combustion engine during the expansion cycle. However, the water is not mixed with the fuel, is not pressurized and is not evaporated.
Last but not least a proposal is known, where water and fuel are injected alternately into the combustion chamber during consecutive work phases. This affords two injection valves. The goal is to reach an improved NO.sub.x -binding with condensed water. Proposals such as the aforementioned are described in German references DE 35 17 177-A and DE 31 43 605-A. The problem of operating a combustion engine with spark ignition with a compressed fuel-vapor-water-vapor-mixture is the increasing knock tendency due to auto-ignition. According to German reference DE 40 35 064-A it is proposed to oppose this tendency by cooling the fuel-vapor-water-vapor-mixture before injection to condense at least a part of the fuel vapor and also the water vapor. This suggestion reduces the thermal efficiency of the combustion engine.
All known proposals trace the same goal to reduce exhaust emissions, especially smoke particles, NO or CO by adding atomized water or water vapor. During injection of the fuel-vapor-water-vapor-mixture just-those pressures and temperatures were allowed, which lead to superheating of the vapor mixture, but still hold the knock tendency of the engine within allowed limits.